The present invention relates to a method for assembling an electrochemical cell and, more particularly, to a method for assembling a primary electrochemical cell having a carbon cathode structure.
Primary electrochemical cells are utilized for a wide variety of applications and are commonly available in a large assortment of sizes and shapes. Furthermore, a number of electrochemical systems are known for incorporation into such primary electrochemical cells. Many of these electrochemical cells utilize a carbon cathode structure. By way of example, in U.S. Pat. No. 4,060,668, in the name of Franz Goebel and assigned to GTE Laboratories Incorporated, there is disclosed an electrochemical system including an anode, a carbon current collector cathode structure, and an electrolytic solution in contact with the anode and the carbon current collector cathode structure. The carbon current collector cathode structure employed in this electrochemical system includes a preformed porous cylindrical carbon structure of a specified length (as determined by the size of the cell), and a twisted metal cathode current collector impressed into and along the carbon structure. One end of the twisted current collector, which protrudes out of the carbon structure, is welded to a feedthrough provided in a cover of the cell. The carbon structure comprises an aggregation of a large number of porous semi-rigid globules which are pressed together in a manner to define a multiplicity of electrolyte-conducting channels. By virtue of these channels, the electrolytic solution can diffuse throughout the porous carbon structure and contact the cathodic particles of the structure.
While carbon current collector cathode structures as described hereinabove can be constructed and successfully employed within electrochemical cells, they nonetheless are subject to numerous possible problems and disadvantages. More particularly, the preformed porous carbon structures are inherently fragile and susceptible to breaking or falling apart when a twisted metal cathode current collector is inserted into the preformed carbon structure, either by twisting or forcing the metal cathode current collector longitudinally into the preformed carbon structure. In addition, the impressing of the twisted current collector into the carbon structure cannot be controlled with great accuracy, especially in positioning and guiding the current collector into and along the center of the carbon structure. As a result, the mechanical and electrical contact between the twisted metal cathode current collector and the preformed carbon structure may be inadequate to satisfy the stringent requirements and specifications of the electrochemical cell in which such structure is to be used.
Carbon current collector cathode structures of alternative design are described in U.S. Pat. No. 4,154,906. The carbon current collector cathode structures disclosed in this patent comprise two or more elongated arcuate carbon bodies which are mechanically biased outwardly by means of a metal member positioned intermediate to, or embedded within, the carbon bodies. The metal member may variously take the form of a coil disposed within an axial opening between the carbon bodies or physically embedded within the carbon bodies, a U-shaped spring strip disposed between or embedded within the carbon bodies and having a protruding end thereof welded to a cover of the cell, or a U-shaped spring strip embedded within the carbon bodies and having the central portion thereof welded to a cover of the cell.
The various carbon current collector cathode structures as described in U.S. Pat. No. 4,154,906 generally have the disadvantage of being difficult to manufacture, especially the embedding of spring members within carbon bodies, and are further difficult to assemble without subjecting the carbon bodies to damage, as by breaking or falling apart.